Surfactant preparations comprising α-hydroxy acids

ABSTRACT

A process for enhancing skin, mucous membranes and textile compatibility with an anionic surfactant composition involving: (a) providing an anionic surfactant composition; (b) providing an acid selected from the group consisting of a hydroxycarboxylic acid, a salt of a hydroxycarboxylic acid, an ester of a hydroxycarboxylic acid with an ethoxylated alcohol, and mixtures thereof; and (c) mixing (a) and (b).

BACKGROUND OF THE INVENTION

This application is a 371 of PCT/EP02/05587 filed May 22, 2002.

This invention relates to surfactant preparations containing α-hydroxyacids which are distinguished by improved dermatological and mucousmembrane compatibility and to the use of hydroxycarboxylic acids and/orsalts and/or esters thereof with ethoxylated alcohols for reducing theirritation potential of surfactants.

In the development of new surfactants, practical consumer protection isthe primary consideration. Time and again, surfactants with very goodperformance properties have been found not to meet the criteria of localcompatibility. Anionic surfactants in particular are known to have ahigh irritation potential [Kästner, W. and Frosch, J. P.,Hautirritationen verschiedener anionaktiver Tenside imDuhring-Kammer-Test am Menschen im Vergleich zu in vitro undtierexperimentellen Methoden in Fette, Seifen, Anstrichmittel 83, 1981,pages 33-46]. Local compatibility is said to be dependent upon the Cchain length and the degree of ethoxylation. Chain lengths of 10 to 14carbon atoms and surfactants with a low degree of ethoxylation show poordermatological compatibility. Although this knowledge can be embraced inproduct development, a loss of favorable performance properties oftenhas to be accepted.

Accordingly, there is still a need on the market even today—despite alarge number of highly compatible surfactants—for substances whichcombine these properties with one another and, despite favorabledetersive properties, compatibility with other auxiliaries and optimalprocessing behavior—also show very good dermatological compatibility.

Accordingly, the problem addressed by the present invention was toreduce the irritation potential of surfactants and to providepreparations containing anionic surfactants which would have highsurface activity but which would still show improved compatibility withthe skin, mucous membrane and textiles.

DESCRIPTION OF THE INVENTION

The present invention relates to the use of hydroxycarboxylic acidsand/or salts and/or esters thereof with ethoxylated alcohols forimproving the compatibility of anionic surfactants with the skin, mucousmembrane and textiles, characterized in that hydroxycarboxylic acidsand/or salts and/or esters thereof with ethoxylated alcohols are addedto the surfactants or surfactant solutions.

The present invention also relates to preparations containing

-   (a) anionic surfactants and-   (b1) 0.1 to 20% by weight α-hydroxycarboxylic acids and/or salts    thereof and/or-   (b2) 25 to 50% by weight of esters of α-hydroxycarboxylic acids with    ethoxylated alcohols, based on the quantity of anionic surfactants,    characterized in that they have a surface activity of at least 20    mN/m (as measured at room temperature by the Wilhelmy plate method    (platinum plate T11 to DIN 53914) and in that they have a Q value in    the HET-CAM test of less than 75%, based on the surfactant solution    without α-hydroxycarboxylic acid.

It has surprisingly been found that the addition of hydroxycarboxylicacids and/or salts thereof and/or esters thereof with ethoxylatedalcohols to anionic surfactants greatly reduces the irritation potentialof the surfactants and hence considerably improves their compatibilitywith the skin, mucous membrane and textiles without any loss ofdetersive activity.

Preparations containing anionic surfactants in combination with 0.1 to20% by weight of α-hydroxycarboxylic acids and/or salts and/or estersthereof with ethoxylated alcohols show considerably better compatibilitythan the pure surfactant formulations as reflected in the fact that thereaction time value in the HET-CAM test can be improved by at least 25%,based on the starting value of the pure surfactant formulation. Thisresult had not be expected because, in antimicrobial detergents inparticular, antimicrobial agents and anionic surfactants are combinedwith carboxylic acids to achieve better antimicrobial activity. The acidis said to reduce the negative charge of the bacterial cell walls andeasily to overcome the cell membrane—weakened by the surfactant—in orderto shift the pH in the cytoplasm of the cell (cf. International patentapplication WO 98/55093, page 10). This is a mechanism which, applied tothe cells of human skin, certainly does not suggest high compatibility.

HET-CAM Test

The HET-CAM test (hen's egg test/chorioallantois membrane test) is atest for determining the acute mucous-membrane-irritating effect ofsubstances on the vascular system of the chorioallantois membrane (CAM)of fertilized hens' eggs incubated for 10 days [Köszegi, Dunja et al.:Der HET-CAM-Test, Euro Cosmetics 11/12-99, pp. 29-33, Künstler, Klaus:Alternative Methoden in der Industrie am Beispiel der Haut-undSchleimhautverträglichkeitsprüfung in Schuppan/Hardegg, Tierschutz durchAlternativen, Gustav Fischer Verlag, Stuttgart 1988].

The chorioallantois membrane which develops during incubation containsan efficient vascular system. It is exposed by removing the egg shellabove the air chamber and covered with 300 μl of the solution to betested. The reactions of the vascular system to the substances areobserved for up to 300 seconds. The degree of irritation is evaluatedaccording to type and onset time. The reaction time is the time inseconds between application and appearance of the reaction parameter.Hemorrhage (bleeding), lysis (dissolving of the blood vessels) andcoagulation (congealing of the egg white) are evaluated as reactionparameters. Through the reaction time, an irritation value [Q] is drawnup as a measure of the particular test substance by comparison with areference substance (Texapon ASV, 5% active substance).

Irritation value [Q] Degree of irritation    0.8 Mildly irritating ≦0.8< 1.2 Moderately irritating ≧1.2 < 2.0 Irritating ≧2.0 Highly irritating

According to the present invention, the addition of hydroxycarboxylicacids and/or salts and/or esters thereof with ethoxylated alcohols isintended considerably to reduce the irritation potential of anionicsurfactants. After addition of the acid and/or salt and/or ester thereofwith ethoxylated alcohols, the Q value of the surfactant preparationwithout hydroxycarboxylic acid is intended to be only 75% of thestarting value. A reduction to 70% of the value of thehydroxycarboxylic-acid-free formulation is preferred and a reduction to65% of that value is particularly preferred.

Determination of Surface Activity

Surface activity was determined to DIN 53914. To this end, the solutionto be tested was tested by the Wilhelmy plate method (plate PT 11) at21±1° C. The preparations according to the invention are intended tohave a surface activity of at least 20 mN/m, preferably at least 25 mN/mand more particularly at least 30 mN/m, based on the active substancecontent of 5% by weight.

Anionic Surfactants

Typical examples of anionic surfactants of the preparations according tothe invention are soaps, alkyl benzenesulfonates, alkane sulfonates,olefin sulfonates, alkyl ether sulfonates, glycerol ether sulfonates,α-methyl ester sulfonates, sulfofatty acids, alkyl sulfates, fattyalcohol ether sulfates, glycerol ether sulfates, fatty acid ethersulfates, hydroxy mixed ether sulfates, monoglyceride (ether)sulfates,fatty acid amide(ether)sulfates, mono- and dialkyl sulfosuccinates,mono- and dialkyl sulfosuccinamates, sulfotriglycerides, amide soaps,ether carboxylic acids and salts thereof, fatty acid isethionates, fattyacid sarcosinates, fatty acid taurides, N-acylamino acids such as, forexample, acyl lactylates, acyl tartrates, acyl glutamates and acylaspartates, alkyl oligoglucoside sulfates, protein fatty acidcondensates (particularly wheat-based vegetable products) andalkyl(ether) phosphates. If the anionic surfactants contain polyglycolether chains, the polyglycol ether chains may have a conventionalhomolog distribution, although they preferably have a narrow homologdistribution. However, preferred anionic surfactants in the preparationsaccording to the invention are alkyl sulfates, fatty alcohol ethersulfates, alkane sulfonates and alkyl sulfosuccinates (among which thealkyl and/or alkenyl sulfates are particularly preferred) and the alkylether sulfates.

Alkyl and/or alkenyl sulfates, which are often also referred to as fattyalcohol sulfates, are understood to be the sulfation products of primaryalcohols which correspond to formula (I):R²O—SO₃X  (I)in which R² is a linear or branched, aliphatic alkyl and/or alkenylgroup containing 6 to 22 carbon atoms and preferably 12 to 18 carbonatoms and X is an alkali metal and/or alkaline earth metal, ammonium,alkyl ammonium, alkanolammonium or glucammonium. Typical examples ofalkyl sulfates which may be used in accordance with the invention arethe sulfation products of caproic alcohol, caprylic alcohol, capricalcohol, 2-ethyl hexyl alcohol, lauryl alcohol, myristyl alcohol, cetylalcohol, palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleylalcohol, elaidyl alcohol, petroselinyl alcohol, arachyl alcohol,gadoleyl alcohol, behenyl alcohol and erucyl alcohol and the technicalmixtures thereof obtained by high-pressure hydrogenation of technicalmethyl ester fractions or aldehydes from Roelen's oxo synthesis. Thesulfation products may advantageously be used in the form of theiralkali metal salts and particularly their sodium salts. Alkyl sulfatesbased on C_(16/18) tallow fatty alcohols or vegetable fatty alcohols ofcomparable C chain distribution in the form of their sodium salts areparticularly preferred.

Alkyl ether sulfates (“ether sulfates”) are known anionic surfactantswhich, on an industrial scale, are produced by SO₃ or chlorosulfonicacid (CSA) sulfation of fatty alcohol or oxoalcohol polyglycol ethersand subsequent neutralization. Ether sulfates suitable for use inaccordance with the invention correspond to formula (II):R¹O—(CH₂CH₂O)_(m)SO₃X  (II)in which R¹ is a linear or branched alkyl and/or alkenyl radicalcontaining 6 to 22 carbon atoms, m is a number of 0 or 1 to 10 and X isan alkali metal and/or alkaline earth metal, ammonium, alkylammonium,alkanol-ammonium or glucammonium. Typical examples are the sulfates ofaddition products of on average 1 to 10 and more particularly 2 to 5 molethylene oxide onto caproic alcohol, caprylic alcohol, 2-ethylhexylalcohol, capric alcohol, lauryl alcohol, isotridecyl alcohol, myristylalcohol, cetyl alcohol, palmitoleyl alcohol, stearyl alcohol, isostearylalcohol, oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, arachylalcohol, gadoleyl alcohol, behenyl alcohol, erucyl alcohol and brassidylalcohol and technical mixtures thereof in the form of their sodiumand/or magnesium salts. The ether sulfates may have both a conventionalhomolog distribution and a narrow homolog distribution. It isparticularly preferred to use ether sulfates based on adducts of onaverage 1.5 to 2.5 mol ethylene oxide with technical C_(12/14) orC_(12/18) coconut fatty alcohol fractions in the form of their sodiumand/or magnesium salts.

The anionic surfactants are present in the preparations according to theinvention in quantities of 1 to 99% by weight, preferably in quantitiesof 2 to 30% by weight and more particularly in quantities of 10 to 20%by weight, based on the quantity of active substance.

Accordingly, the present invention also relates to preparationscontaining

-   (a) 2 to 30% by weight anionic surfactants and-   (b1) 0.1 to 20% by weight α-hydroxycarboxylic acids and/or salts    thereof and/or-   (b2) 25 to 50% by weight of esters α-hydroxycarboxylic acids with    ethoxylated alcohols, based on the quantity of anionic surfactants,    characterized in that they have a surface activity of at least 20    mN/m (as measured at room temperature by the Wilhelmy plate method    (platinum plate T11 to DIN 53914) and in that they have a Q value in    the HET-CAM test of less than 75%, based on the surfactant solution    without α-hydroxycarboxylic acid.    Hydroxycarboxylic Acids and Salts and Esters thereof with    Ethoxylated Alcohols

Hydroxycarboxylic acids are organic acids which, besides at least oneCOOH group, contain at least one OH group in the molecule. With one OHgroup, they may be present as monohydroxycarboxylic acids, with two OHgroups as dicarboxylic acids or, with more than two OH groups, aspolyhydroxycarboxylic acids. Hydroxycarboxylic acids are referred to asα-, β- and γ-hydroxycarboxylic acids according to the position of the OHgroup to the COOH group. The acids may be saturated or unsaturated(example: ricinoleic acid). Known aromatic hydroxycarboxylic acids aresalicylic acid (2-hydroxybenzoic acid) and gallic acid(3,4,5-trihydroxybenzoic acid).

According to the present invention, preferred hydroxycarboxylic acidsare α-hydroxycarboxylic acids, more particularly tartaric acid, mandelicacid, lactic acid, malic acid, citric acid and salts thereof.

The preparations according to the invention contain 0.1 to 20% byweight, preferably 1 to 15% by weight and more particularly 5 to 10% byweight of α-hydroxycarboxylic acids and/or salts thereof, based on thequantity of anionic surfactants.

The esters of the hydroxycarboxylic acids with ethoxylated alcohols areknown compounds which correspond to formula (III):R³-(EO)_(x)-Z  (III)in which R³ is an alkyl group containing 6 to 22 carbon atoms andpreferably 12 to 14 carbon atoms, X is an integer of 1 to 20 andpreferably 2 to 10 and Z is a hydroxycarboxylic acid residue. Accordingto the invention, preferred hydroxycarboxylic acids as the residue Z arehydroxycarboxylic acids, more particularly tartaric acid, mandelic acid,lactic acid, malic acid, citric acid.

The preparations according to the invention contain 25 to 50% by weightof esters of the hydroxycarboxylic acids with alkyl ethoxylates, basedon the quantity of anionic surfactants.

Commercial Applications

The preparations according to the invention are intended to be used—butnot exclusively—for the production of cosmetic preparations, dental carepreparations, laundry detergents, dishwashing detergents and cleaners.

The preparations according to the invention containing anionicsurfactants in combination with α-hydroxycarboxylic acids and/or saltsand/or ester thereof with ethoxylated alcohols may contain any productsthrough which the skin may come into contact with anionic surfactants inorder to reduce the risk of irritation.

Depending on the particular application envisaged, the preparationsaccording to the invention may contain other auxiliaries, but notantimicrobial agents. They may be present in solid form but arepreferably present in the form of an aqueous or alcoholic/aqueoussolution. The pH value of the preparations should be between pH 4 and pH7 and is preferably between pH 5 and pH 6.8 and more particularlybetween pH 6 and pH 6.6.

For cosmetic and/or pharmaceutical applications, they may contain othermild surfactants, emulsifiers, lipid layer enhancers, pearlizing waxes,consistency factors, thickeners, superfatting agents, stabilizers,polymers, silicone compounds, fats, waxes, lecithins, phospholipids,biogenic agents, UV protection factors, antioxidants, deodorants,antiperspirants, antidandruff agents, film formers, swelling agents,insect repellents, self-tanning agents, tyrosine inhibitors(depigmenting agents), hydrotropes, solubilizers, preservatives, perfumeoils, dyes and the like as further auxiliaries and additives.

If the surfactant mixtures according to the invention are used for theproduction of detergents, the preparations may contain other typicalingredients such as, for example, solvents, hydrotropes, bleachingagents, bleach activators, detergency boosters, builders, viscosityadjusters, enzymes, enzyme stabilizers, optical brighteners, soilrepellents, foam inhibitors, inorganic salts and perfumes and dyes.

EXAMPLES

Determination of Surface Tension

The surface tension of the surfactant solution containing tartaric acidwas compared with that of the pure surfactant solution (Texapon® NSO,sodium lauryl ether sulfate; Cognis, Dusseldorf) by conductingmeasurements at 21±1° C. using the Wilhelmy plate method (plate PT 11)to DIN 53914.

TABLE 1A Surface tension of the surfactant solution containing tartaricacid and the pure surfactant solution Substance Concentration Surfacetension Texapon ® NSO   5% by weight active substance  31.6 mN/m sodiumlauryl ether sulfate Texapon ® NSO with   5% by weight active substance30.03 mN/m tartaric acid sodium lauryl ether sulfate 0.5% by weighttartaric acidDetermination of Foaming Behavior

To determine foaming behavior, the foaming kinetics after 30 seconds andthe foam potential after 60 s and 180 s were measured by the rotor foammethod (DIN 13996 in preparation). The rotor foam tester consists of aheatable, double-walled cylindrical glass vessel with an internaldiameter of 17.5 cm. A scale in mm is provided on the cylindrical glassvessel for reading off the foam height and the liquid level. Inaddition, the glass vessel is provided with a Styropor lid which is usedboth to cover and to insulate the vessel. The stirrer consists of aspecial stirring head with a stirrer shaft 28 cm in length and 1 cm indiameter and a JK stirrer with a digital revolution counter. Athermostat, a stopwatch and a thermometer (digital) are also required.

The test solution was prepared with water of a certain hardness (15°dH). 200 ml of the sample preheated to 30±1° C. were slowly poured in atthe rim of the glass vessel which was covered with the Styropor lid whenthe required temperature of 30±1° C. had been reached. The rotor speedwas 1300 r.p.m.

The first foam height value was determined after 30 seconds. To thisend, the stirrer was switched off for at most 10 seconds. The foamvolume was then determined after 60 and 180 seconds.

TABLE 1b Foam behavior of the surfactant solution containing tartaricacid and the pure surfactant solution Substance Concentration Foambehavior Texapon ® NSO  0.1% by weight active 30 s 10.8 cm substancesodium lauryl 60 s 11.0 cm ether sulfate 180 s  11.0 cm Texapon ® NSO 0.1% by weight active 30 s 10.8 cn  with tartaric acid substance sodiumlauryl 60 s 11.0 cm ether sulfate 0.01% by weight tartaric acid 180 s 11.0 cm Texapon ® NSO with  0.1% by weight active 30 s  9.5 cmlaureth-4-citrate substance sodium lauryl 60 s 10.8 cm ether sulfate0.01% by weight laureth-4- 180 s  11.0 cm citrate

It is clear from the test results (Tables 1a and 1b) that the additionof tartaric acid or lareth-4-citrate does not significantly affect thesurface activity or the foam behavior of the anionic surfactant so thatit may be assumed that the addition of tartaric acid orlaureth-4-citrate does not reduce the detersive performance of thesurfactant although the irritation potential is reduced.

Determination of the Irritation Potential—In Vitro Test: HET-CAM Test,Reaction Time Method

The irritation potential was determined by a HET-CAM test as describedin “Der HET-CAM-Test”, Euro Cosmetics 11/12-99, pp. 29-33, Dunja et al.

TABLE 2 Reaction time method and end point evaluation by the HET-CAMtest Reaction time Substance Concentration [Q value] Texapon ® ASV   5%by weight active substance 1.00 mixture of special mild fatty alcoholether sulfates Texapon ® NSO   5% by weight active substance 1.63 sodiumlauryl ether sulfate Texapon ® NSO   3% by weight active substance 1.47sodium lauryl ether sulfate  0.5% by weight tartaric acid Texapon ® NSOwith   5% by weight active substance 1.01 tartaric acid sodium laurylether sulfate  0.5% by weight tartaric acid Texapon ® NSO with 3.75% byweight active substance 0.95 laureth-4-citrate sodium lauryl ethersulfate 1.25% by weight laureth-4-citrate

The results (Table 2) show a distinct reduction in the irritationpotential of anionic surfactants by the addition of tartaric acid orlaureth-4-citrate. The reaction time [Q value] is reduced to 62% of theoriginal value by the addition of 10% by weight tartaric acid (based onthe quantity of anionic surfactants) and to as low as 58% of theoriginal value by the addition of 33% laureth-4-citrate (based on thequantity of anionic surfactants).

1. A process for improving the compatibility of a composition comprisinganionic surfactants with skin, mucous membrane and tissue, whichcomprises: incorporating a compatibility improving amount of anethoxylated alcohol ester of a hydroxycarboxylic acid of formula:R³O—(EO)_(X)—Z  (III) wherein, R³ is an alkyl group containing 6 to 22carbon atoms, (EO) is an ethoxy group, x is an integer of 1 to 10, and Zis a hydroxycarboxylic acid residue, into the composition comprising theanionic surtactant, whereby, the compatibility of the compositioncomprising the anionic surfactant is improved when compared to acomposition which does not contain the ethoxylated alcohol ester of thehydroxycarboxylic acid.
 2. The process of claim 1, wherein, 25 to 50% byweight, based on a quantity of anionic surfactants, of esters ofα-hydroxycarboxylic acids with ethoxylated alcohols are incorporatedinto the composition.
 3. The process of claim 1 wherein, the compositioncomprising anionic surfactants further comprises at least one memberselected from the group consisting of other mild surfactants,emulsifiers, lipid layer enhancers, pearlizing waxes, consistencyfactors, thickeners, superfatting agents, stabilizers, polymers,silicone compounds, fats, waxes, lecithins, phospholipids, biogenicagents, UV protection factors, antioxidants, deodorants,antiperspirants, antidandruff agents, film formers, swelling agents,insect repellents, self-tanning agents, tyrosine inhibitors(depigmenting agents), hydrotropes, solubilizers, preservatives, perfumeoils, dyes and further auxiliaries and additives.
 4. The process ofclaim 1 wherein R³ contains from 12 to 14 carbon atoms.
 5. The processof claim 1 wherein x is an Integer of from 2to
 10. 6. The process ofclaim 1 wherein, Z comprises a residue of at least one acid selectedfrom the group consisting of tartaric acid, mandelic acid, lactic acid,malic acid and citric acid.
 7. The process of claim 1, wherein, Z is aresidue of an α-hydroxycarboxylic acid.
 8. A composition comprising: ananionic surfactant and 25% to 50% by weight, based on weight of theanionic surfactant, of an ethoxylated alcohol ester of ahydroxycarboxylic acid of formula:R³O—(EO)_(x)—Z  (III) wherein. R³ is an alkyl group containing 6 to 22carbon atoms. (EO) is an ethoxy group. X is an integer from 1 to 10, andZ is a hydroxycarboxylic acid residue.
 9. The composition of claim 8,wherein, x is an integer of from 2 to
 10. 10. The composition of claim 8further comprising at least one member selected from the groupconsisting of other mild surfactants, emulsifiers, lipid layerenhancers, pearlizing waxes, consistency factors, thickeners,superfatting agents, stabilizers, polymers, silicone compounds, fats,waxes, lecithins, phospholipids, biogenic agents, UV protection factors,antioxidants, deodorants, antiperspirants, antidandruff agents, filmformers, swelling agents, insect repellents, self-tanning agents,tyrosine inhibitors (depigmenting agents), hydrotropes, solubilizers,preservatives, perfume oils, dyes and the-like-as further auxiliariesand additives.
 11. The composition of claim 8, wherein, the compositionhas a surface activity of at least 20 mN/in (as measured at 21±1° C. byDIN 53914 method) and a Q value of less than 75% in the HET-CAM Testbased on a surfactant solution comprising the anionic surfactant withoutthe ethoxylated alcohol ester of the hydroxycarboxylic acid.
 12. Thecomposition of claim 8, wherein, the hydroxycarboxylic acid residuecomprises at least one residue of an acid selected from the groupconsisting of tartaric acid, mandelic acid, lactic acid, malic acid andcitric acid.
 13. The composition of claim 8, wherein, the ester of thehydroxycarboxylic acid comprises an ester of an α-hydroxycarboxylicacid.